1. Field of the Invention
The invention relates to a translation and rotation positioning motor, which can be used for providing precise linear and rotational movements of a scanning tunneling microscope, for example. In particular, the invention relates to a translation and rotation positioning motor that includes piezo actuators and that provides for movement of an object by angstrom level or sub-angstrom level increments on one or more planes, and that is capable of repeated precise realignment of the object so that it can be moved repeatedly to a desired position.
2. Description of the Related Art
Scanning tunneling microscopes (STM) are widely used in industry and in research to obtain atomic-scale images of specimen surfaces. An STM provides a three-dimensional profile of the surface, which is useful for characterizing surface roughness, observing surface defects, and determining surface structure with atomic resolution. An STM operates by providing a needle point of the STM in very close proximity to the specimen surface to be scanned, whereby the needle point is moved about the surface in a raster-like manner. The needle point is disposed at a distance from the specimen surface so that a tunneling effect is achieved, whereby, when a voltage is provided to the needle point, electrons “tunnel” from the needle point to the specimen surface. By moving the needle point with respect to an opposite point on the specimen surface in order to obtain a particular current flow, a plot of the specimen surface characteristic at that point is obtained. By rastering the needle point about different parts of the specimen surface, a three dimensional plot of the specimen surface is obtained.
In order to bring the needle point of the STM close enough (but not in contact) to the specimen surface to achieve the desired tunneling effect, the needle point is moved by way of a coarse positioning device of the STM. Once in the “tunneling region”, a fine positioning device of the STM is utilized in order to obtain a precise positioning of the needle point with respect to the specimen surface to be scanned.
One such positioning device that allows for microscopic movements of a scanning tunneling microscope, and that can be used as either a coarse adjusting device or as a fine adjusting device for an STM, is described in U.S. Pat. No. 5,237,238, issued to Thomas Berghaus et al., which is incorporated in its entirety herein by reference. The Berghaus et al. patent describes various types of positioning devices, some of which allow for both linear and rotational movement of an element. FIGS. 15 and 15a of the Berghaus et al. patent show a first adjusting device that allows for both linear and rotary movement of a turntable. Referring now to FIG. 15d of the Berghaus et al. patent, rotary movement of a turntable 5 is accomplished by way of drive elements 6a and 6b, each of which includes a bearing element. Linear movement of the turntable 5 is accomplished by way of drive element 6c, which is fitted within a groove 34 on the bottom surface of the turntable 5.
FIG. 17 of the Berghaus et al. patent shows a second adjusting device that allows for both linear and rotary movement. Rotary movement of a turntable 5 is accomplished by way of a rotary adjusting device 1, while linear movement of the turntable 5 is accomplished by way of a linear adjusting device 1′ (which has a bearing element of triangular cross-section).
Another conventional microscopic adjusting device is described in published European Patent Application WO 93/19494, by Shuheng Pan, which is incorporated in its entirety herein by reference. The Pan apparatus provides for microscopic movement of an object in a step-by-step manner, whereby piezo actuators (elements 2a-2d as shown in FIG. 1a of Pan) are moved individually (or in groups) in one direction successively while the remaining actuators hold the object still, and when all of the actuators have been moved, they are simultaneously moved in the opposite direction. The simultaneous movement of the actuators in the opposite direction results in linear movement of the object. Different embodiments described by Pan include an embodiment shown in FIG. 5 of Pan, which allows for rotational movement of a sphere 50 about a center point of the sphere.
None of the conventional microscopic adjusting devices described above allows for x-y-z movement of an object using a single adjusting device that provides the capability of movement of the object in both a linear direction and a rotational direction.
Also, the geometrical structure of objects being moved in the apparatuses of Berghaus and Pan are not believed by the inventors of this application to be ideal for allowing rotational and linear movement of an object.